1. Field of the Invention
Methods and apparatuses consistent with the present invention relate to a signal transmission and reception over a wireless network and a reader. More particularly, the present invention relates to a method of transmitting and receiving a signal over a wireless network and a reader using a pulse width list of a transmission (Tx) signal to improve communication efficiency.
2. Description of the Related Art
FIG. 1 depicts a simplified construction of a wireless network system according to the related art. The wireless network system of the related art includes a reader 10 and at least one sensing means 20. The sensing means 20 may be a tag or a sensor.
The reader 10 transmits a signal to the sensing means 20. In response to the transmitted signal, the sensing means 20 transmit a signal containing information collected from their environments to the reader 10. However, smooth communications between the reader and the sensing means 20 may be interrupted by the following factors:
A tag collision when the reader 10 receives signals from a plurality of sensing means 20 at the same time, a reader collision when a plurality of readers 10 generates or receives signals at the same time, a sensitivity problem of the reader 10, and an unrecognized signal command received from the reader 10 due to channel conditions of the sensing means 20.
The techniques described here analyze and resolve the degradation of the communication performance when the sensing means 20 cannot recognize the signal command received from the reader 10.
In the related art, when communicating without a channel filter, the reader 10 transmits a transmission (Tx) signal (signal command) to the sensing means 20 using amplitude shift keying (ASK) modulation. The sensing means 20 receives the Tx signal from the reader 10 using envelope detection.
FIG. 2 is a graph showing a spectral mask in a wireless network environment where a plurality of readers is present. To minimize the interference between the readers, the frequency channel and the spectral mask of the channel, as shown in FIG. 2, should be satisfied. Meanwhile, 27 channels are allocated within the domestic frequency range 908.5 MHz˜914 MHz and the channel width for each channel is 200 KHz.
However, if a link frequency is 40 KHz, a transmitter for the reader 10 requires a channel filter to satisfy the spectral mask shown in FIG. 2.
FIG. 3A is a graph showing a signal received at an envelope detector of the sensing means when the reader is not equipped with the channel filter. As one can see in FIG. 3A, the sensing means 20 has almost uniform pulse widths 30 during the envelope detection.
FIG. 3B is a graph showing a signal received at the envelope detector of the sensing means when the reader is equipped with the channel filter. As one can see in FIG. 3B, the sensing means 20 has variable pulse widths 40 in some cases during the envelope detection.
In conclusion, the intensity of the signal received at the sensing means 20 varies according to the distance between the sensing means 20 and the reader 10, the output power of the reader 10, the direction, and the modulation degree of the reader 10. Additionally, the pulse width detected after the envelope detection varies according to the signal intensity of the sensing means 20. Thus, the sensing means 20 cannot recognize the signal command received from the reader 10 because of the above-mentioned factors when the reader 10 is equipped with the channel filter. As a result, the reader 10 does not receive a reply signal from the intended sensing means 20.